Code shared from the Rust Playground

playground.rs

pub trait SigningKey {
    fn create_digest(&self, data: Vec<u8>) -> Vec<u8>;
}

pub struct RsaKey {
    modulus: Vec<u8>,
    exponent: Vec<u8>,
}

impl SigningKey for RsaKey {
    fn create_digest(&self, data: Vec<u8>) -> Vec<u8> {
        // In the real world at this point we'd calculate a SHA1, stick the
        // right DER goop in front of it and return that. Because this is
        // only an example we're just going to return what we got handed.
        Vec::from(data)
    }
}

pub enum EcdsaCurve {
    NistP256,
    NistP384,
    NistP521,
}

pub struct EcdsaKey {
    pub curve: EcdsaCurve,
    pub key_blob: Vec<u8>,
}

impl SigningKey for EcdsaKey {
    fn create_digest(&self, data: Vec<u8>) -> Vec<u8> {
        // See above for an explanation of our horrible lies.
        Vec::from(data)
    }
}

pub enum Key {
    Ecdsa(EcdsaKey),
    Rsa(RsaKey),
}

impl Key {
    fn create_digest(&self, data: Vec<u8>) -> Vec<u8> {
        // How can I call the create_digest method of the variant that I have
        // here without copy/pasting the same match arm all the way down?
        match self {
            Key::Ecdsa(k) => k.create_digest(data),
            Key::Rsa(k) => k.create_digest(data),
            // Oh god I hope I never have to add any more...
        }
    }
}